#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int C, N;
int dp[101][100001];
int a[100];

int solve() {
    rep (i, 101) rep (j, C + 1) dp[i][j] = inf;
    dp[0][0] = 0;

    rep (i, N) {
        rep (j, C + 1) {
            dp[i + 1][j] = min(dp[i + 1][j], dp[i][j]);
            if (j + a[i] <= C) {
                dp[i + 1][j + a[i]] = min(dp[i + 1][j + a[i]], dp[i + 1][j] + 1);
            }
        }
    }

    return dp[N][C];
}

int main() {
    cin >> C >> N;
    rep (i, N) cin >> a[i];
    int ans = solve();
    if (ans == inf) ans = -1;
    cout << ans << endl;
}